In a Hybrid Automatic Repeat Request (HARQ) mode, a code sent by a sender not only can detect errors but also has a certain error correcting capability. After receiving code words, a decoder of a receiver first detects errors, if they are within the error correcting capability of the code, the decoder automatically performs error correction; if there are many errors that exceed the error correcting capability of the code but can still be detected, the receiver sends a decision signal to the sender through a feedback channel, requesting the sender to retransmit information.
In an Orthogonal Frequency Division Multiplexing (OFDM) system, Acknowledged/Non-acknowledged (ACK/NACK) control signaling is used to indicate whether information transmission is correct or incorrect, in this way, it can be judged whether retransmission is necessary.
Currently, it is specified in a Long Term Evolution (LTE) system that an ACK/NACK message related to uplink data is transmitted over a physical hybrid ARQ indicator channel. There are two methods for allocating physical hybrid ARQ indicator channels, one is indicated through explicit signaling, while the other is indicated through implicit mapping, and the latter method does not require extra overhead relative to the former, thus is more advantageous.
There are primarily two methods for the implicit mapping: the first implicit mapping method is that the implicit mapping is performed through an index of a control logic unit where uplink authorization control signaling resides; the second implicit mapping method is that the implicit mapping is performed jointly through the lowest serial number of physical resource blocks where the uplink data resides and cyclic shift of uplink data reference signals. Since an uplink HARQ is synchronous self-adaptive, when retransmitting data, the sender does not require new control signaling to indicate the position where the retransmitted data is sent, but transfers the retransmitted data in a position where the initial transmission was performed, and in a time division duplex system, this may result in a situation that uplink time slots and downlink time slots are not equal because there are many configurations for the ratio of the uplink time slots to the downlink time slots.
During data is retransmitted according to the first implicit mapping method, a situation may occur that the ACK/NACK message of the retransmitted data and the ACK/NACK message of new data are mapped to the same Physical Hybrid ARQ Indicator Channel (PHICH) so that a target user can not acquire the correct ACK/NACK message.
For the second implicit mapping method in a time division duplex system, when the ratio of the uplink time slots to the downlink time slots is 3:1, a situation may occur that the ACK/NACK messages of data in different uplink sub-frames are mapped to the same PHICH so that a target user can not acquire the correct ACK/NACK message.
In view of this, it is necessary to provide a more sophisticated solution to solve the problem of allocating physical hybrid ARQ indicator channels in the time division duplex system.